Eruptive Debris at Taylor s Falls, Minn. — Winchell. jy 
to include in the Keweenawan are divisible into two great 
series separated by a period of quiet in the eruptive activities. 
During this period of comparative quiet was accumulated a 
conglomerate and a quartzyte which reached the thickness 
of several hundred feet. 
What has now been said should be understood as referring 
to a stratum which at Taylor's Falls and elsewhere lies be- 
tween two important series of trap sheets. It has no refer- 
ence to the conglomerate which at Taylor's Falls has a dol- 
omitic or arenaceous cement in which are found Lingula and 
Discina, indicating its Upper Cambrian age and which has 
been frequently mentioned by geologists. The accident that 
this later conglomerate lies directly upon the earlier, at one 
or two of the most favorable exposures, has hitherto con- 
fused the true relations, and has led to the belief that the 
whole conglomerate belongs to the Upper Cambrian. This 
was the view taken by the writer published in the geological 
survey report for 1881 (loth Rep. pp. 117, 118). The differ- 
ences between the matrix of the lower conglomerate and that 
of the upper were pointed out, so far as they could be by field 
observations, but these differences were attributed provision- 
ally to a hypothetical alteration which the bottom of the con- 
glomerate was presumed to have suffered. It was not till 
the recent survey by Mr. Berkey that the entire separation of 
the lower from the upper was established. 
But this chronologic and stratigraphic separation brings 
up another* difficulty, viz: may not the lower conglomerate 
be of the nature of a flow breccia of the igneous rocks? This 
view is that taken by Mr. Berkey in his recent paper pub- 
lished in the American Geologist,* treating of the geology of 
the St. Croix dalles. It must be admitted that outwardlv, 
when the upper surface of the conglomerate has been de- 
nuded by the removal of the overlying grit and tufaceous 
stratum, the rough and rounded masses that present them- 
selves, making a somewhat hummocky appearance, might 
be attributed to the action of a cooled u])per surface of a 
lava flow, brecciated and somewhat rounded by the crowding 
and friction of the still moving molten portion underneath. 
To the writer, however, the difficulties which such an inter- 
*Vol. XX, pp. 345-383, Dec. i8q7. 
